Accurate, noninvasive assessment of brain circulation is needed in numerous neurosurgical procedures, clinical diagnosis of cerebrovascular pathology (e.g., stroke), drug testing and in biological psychiatry. However, currently employed methods not only are very costly but expose patients to radioactive materials. Further, no available methods provide second-to-second (e.g., real time) dynamic measures of cerebrovascular function, greatly restricting the number of applications of these methods. The long term goal of this project is the development of a microcomputer-controlled electrical impedance brain monitor capable of providing accurate, nearly continuous imaging of hemispheric and regional cerebral blood flow noninvasively at less cost than radioisotope-based methods. Phase I is designed to provide two-dimensional spatial calibration of the non-traumatic "rheoencephalographic" (REG) method by comparing it with an established radiological procedure (gamma camera with 133-Xenon inhalation) in healthy volunteer subjects and patients with cerebrovascular disorders. Correlational analysis of impedance-derived and gamma camera data will reveal the two-dimensional shape and area of cortical tissue monitored by pairs of sensing electrodes. At this stage, several accepted flow equations will be compared with the goal of calculating absolute flow values using impedance waveform parameters. Concurrently, a microcomputer-based software will be developed to automatically collect, analyze and format impedance-derived data. This will simplify operation of the system so that it will be useful for clinical as well as experimental applications. Phase II will initially involve development of software to generate two-dimensional images of regional cerebral blood flow, based on Phase I calibration. Subsequently, the complete imaging system will again be compared to radiological methods (PET scans, CT scans) and tested in clinical populations. The successful implementation of the proposed research would provide essential, basic data needed for commercialization.